It has been recognized for some time the benefits of incorporating in textile fibers, materials that have an afterglow effect. The primary benefit is improved safety considerations due to visibility of the fibers in the dark.
Until now, the process used to achieve this objective has been to bind phosphorescent particles to the outer surface of conventional textile fibers. While the advantage of this process is that it is relatively easy to achieve, the primary disadvantage is that the phosphorescent particles can be lost due to abrasion from wear and more significantly can be lost when the fibers are washed.
A feasible solution has been found to both problems. The solution to the problems of abrasion and washfastness, is by introducing the phosphorescent particles in a solution of melted polymer, and extruding to form fibers without the presence of the particles on the surface of the fibers.
Until now, phosphorescent particles have comprised sulfide phosphors, principally zinc sulfide. The afterglow of phosphorescent fibers, comprising these phosphorescent particles, which allows these fibers to be visually recognized in the dark has been limited to less than 200 minutes. This was a limitation, in terms of utilizing these phosphorescent fibers for safety and novelty applications.
Relatively large concentration levels of the zinc sulfide phosphorescent particles were needed to maximize the level of afterglow brightness of the phosphorescent fibers. These concentration levels were between 5% to 10%, by weight, of the polymer in the fiber.
The consequence, in utilizing these large concentration levels of phosphorescent particles, has been to reduce both the tenacity of the fiber and the elongation of the fiber or even interruption of the process of production.
Tests have shown that long-term exposure of these phosphorescent fibers, comprising zinc sulfide phosphorescent pigments, to the sun's ultra-violet rays can reduce the photo resistance of the fibers by 50%.
A feasible solution has been found to the problems associated with the zinc sulfide phosphorescent pigments which is to substitute with a novel phosphorescent phosphor comprising, for example, of alkaline earth metal type aluminate activated by europium or the like. This phosphorescent phosphor shows afterglow characteristics which last much longer than those of currently available zinc sulfide phosphorescent particles and shows superior photo-resistance. Relatively low concentration levels of this phosphorescent phosphor are needed to maximize the afterglow brightness of phosphorescent fibers. These concentration levels are between 1%-3%, by weight, of the polymer in fibers.
The closest prior art to the subject invention that the applicant is aware is disclosed in WADELY, U.S. Pat. No. 2,787,558 and GRAVISSE et al., U.S. Pat. No. 4,211,813 and GOGUEN, U.S. Pat. No. 4,629,583 and DOANE, Jr., U.S. Pat. No. 4,781,647 and TAGUCHI et al., U.S. Pat. No. 5,140,060 and OWENS, U.S. Pat. No. 5,321,069 and MURAYAMA et al., U.S. Pat. No. 5,424,006 and Foreign Patent Nos. to Hahl et al., DE 3328075 and Wakita, DE 3434971 and Servadio, GB 2042578. Wadely teaches a yarn that is immersed in a solution that contains phosphorescent particles with a chemical base substance of zinc sulphide. Gravisse teaches a textile material to which a coating layer is adhered, comprising one or more synthetic resins and a phosphorescent metal sulphide such as zinc sulphide. Both Gravisse and Wadely fail to suggest how to deal with the abrasion and washfastness problems. Hahl et al. claim the preparation of filaments for fishing lines by mixing phosphorescent material with melted thermoplastic material in an extruder. Wakita claims the preparation of luminescent fibres for safety clothing at night by melt-spinning polypropylene spheres with phosphorescent material such as zinc sulfide. Doane Jr. claims a method of mixing a plurality of phosphorescent particles with an unhardened polymeric material and extruding the resultant mixture to form doll hair fibers. Doane Jr. premixes the phosphorescent particles with a coating agent in order to enhance the distribution of the phosphorescent particles in the finished fibers. Hahl et al., Wakita, and Doane Jr. fail to suggest how to deal with the problems of short-term length of luminescence, poor strength of the fibers, poor elasticity of the fibers, and degradation of the fibers' photo resistant capabilities from long-term exposure to the sun's ultra-violet rays. Goguen invents a phosphorescent polymer-containing composition for use in footwear and shoe soles. Taguchi et al. invent the addition of phosphorescent powder, such as zinc sulfide, to a matrix polymer to produce an electroluminescent device. Servadio invents a phosphorescent plastics composition comprising the pigment zinc sulfide to produce flexible labels. Goguen, Taguchi et al., and Servadio also fail to suggest how to deal with the problems of short-term length of luminescence, and degradation of the phosphorescent pigment, zinc sulfide, photo resistant capabilities from long-term exposure to the sun's ultra-violet rays. Owens invents a process for producing phosphorescent yarn utilizing a suitable wetting agent, such an oil, to coat each pellet of the polymer to be used, in a mixer or tumbler, and then adding the phosphorescent powder and tumbling until the powdered pigment adheres uniformly to each pellet in the mixer. The material is then fed to an extruder where it is processed in the conventional manner to melt the polymer and to thoroughly mix the phosphorescent material throughout the melt. Owens claims that his process enables a highly uniform distribution of phosphorescent material throughout the melt and enables operation of commercial melt spinning apparatus with a high loading of phosphorescent material, zinc sulfide pigment, and enables the production of a highly uniform product having characteristics suitable to produce a high grade commercial phosphorescent textile product. Owens fails to suggest how to produce a yarn product with a denier per filament of less than five which excludes virtually all apparel yarn. Owens fails to suggest how to produce a Nylon BCF yarn that has the physical characteristics of standard tenacity (2.5) and standard elongation (35%). Owens fails to suggest how his invention prevents the problem of the phosphorescent particles from collecting to each other, due to friction causing static electricity, before the particles are adhered to the polymeric pellets causing the filtration screens in the extruder systems to become plugged and interrupting the process of yarn production entirely in some instances. Murayama et al. describe a metal oxide phosphorescent phosphor that is an improvement to sulfide phosphors in terms of the time length of maximum luminescence, the level of after-glow brightness, and the photo-resistance to the ultra-violet rays in both natural and artificial light. The phosphorescent phosphor described by Murayama et al. may be coated on the surface of various products and may be mixed into a plastic material, rubber or glass. Murayama et al. fail to suggest how to sieve, or filter, the phosphorescent phosphor finer than a 100 mesh (150 micron) sieve which limits the possible applications. Murayama et al. fail to suggest how to prevent the phosphor particles from collecting to each other, due to friction causing static electricity when sieved or filtered, and thereby plugging the filtration screens of an extrusion system when the phosphors are mixed into a plastic material. Murayama et al. fail to suggest that when mixing the phosphorescent phosphor into plastic material that two entry ports should be used, one for the polymeric material resin and one for the phosphorescent phosphor into the melted polymeric material. Due to the metallic composition of the phosphor, the phosphor particles are a hard substance whose abrasiveness could damage the extrusion equipment if mixed directly with the polymeric material pellets. Murayama et al. fail to suggest the mixing of this phosphorescent phosphor in a melt solution comprising a polymer known for producing textile fibers such as polyester, PET or PBT. Murayama et al. also fails to suggest the extrusion of textile fibers from this composition of materials as a possible application utilizing this phosphorescent phosphor. Therefore, Murayama et al. is believed to be of only general interest in the context of the subject invent ion.